customizeSegment method
To customize each segments.
Implementation
@override
void customizeSegment(ChartSegment segment) {
  final HistogramSegment<T, D> histogramSegment =
      segment as HistogramSegment<T, D>;
  updateSegmentTrackerStyle(
    histogramSegment,
    trackColor,
    trackBorderColor,
    trackBorderWidth,
  );
  updateSegmentColor(histogramSegment, borderColor, borderWidth);
  updateSegmentGradient(
    histogramSegment,
    gradientBounds: histogramSegment.segmentRect?.outerRect,
    gradient: gradient,
    borderGradient: borderGradient,
  );
}